LVDT calibration using a phase modulation optical interferometer calibrated by an x-ray interferometer

We have calibrated an LVDT using an optical and x-ray interferometer. We have calibrated optical interferometer using x-ray interferometer. The LVDT has calibrated by the optical interferometer. We made the monolithic x-ray interferometer with a double parallel spring structure for the translation of an analyzer lamella. One period of the x-ray interference fringe corresponds to the lattice parameter, 0.192 nm. The nonlinearity of optical interferometer has been calibrated by an x-ray interferometer. We have used a phase modulation optical interferometer. This calibration using the x-ray interferometer is directly traceable to primary standards. We have achieved the resolution of an x-ray interferometer and optical interferometer better than 0.01 nm. The optical phase stability of the interferometer is less than ± 150 pm. For the control of environmental temperature, we have used PID method. PID controller controlled the temperature inside chamber. Temperature drift was less than ± 3 mK ( k = 2).